1. Field of the Invention
The present invention relates to synchronous motors and synchronous motor control circuits for controlling the electric signals supplied to the motor to drive the rotor. More particularly, the present invention relates to synchronous motor control circuits capable of generating phase timing signals that are supplied to the respective stator coils, which signals are generated based upon output signals of a rotor position detector.
2. Description of the Related Art
FIG. 5 shows a known switched reluctance motor (xe2x80x9cSR motorxe2x80x9d) or commutator-less motor. This SR motor is a 6-4-pole three-phase SR motor having a stator and a rotor. The stator includes a stator core with six stator poles 51-56 that are physically spaced at 60xc2x0 intervals, which corresponds to electrical angles of 120xc2x0. Coils are wound around the respective stator poles 51-56. Coils wound around two opposing stator poles are electrically connected in series to provide an opposing pair of stator coils that will be energized by the same control signal. For example, the coils wound around stator poles 51 and 54 are connected with each other in series. The three sets of electrically coupled coils are respectively energized in each of the respective three phases, i.e., U-phase, V-phase and W-phase.
The rotor 64 has a rotor core 65 with a rotating axis and magnetic rotor poles 57 projecting from the outer periphery of the rotor core 65. The magnets in the rotor 64 create eight magnetic regions 58, which each cover 45xc2x0 intervals of the rotor 64.
A control circuit (not shown) controls the timing of the rotor drive (control) signals that are supplied to the stator coils for each of the respective three phases. The timing signals are generated based upon output signals from rotor position detectors. The control circuit generates rotor driving signals that cause the rotor to rotate either in a forward direction or a reverse direction. The known control circuit uses Hall ICs 63u, 63v and 63w as the rotor position detectors, which Hall ICs contain Hall elements for detecting the magnetic field of the rotor magnetic regions 58. A Hall IC (63u, 63v and 63w) is located at a central position of each stator pole (U-phase stator pole 51, V-phase stator pole 56 and W-phase stator pole 52, respectively).
FIG. 6 shows a timing chart with timing signals of a type suitable for driving a typical SR motor. This timing chart shows the relationship between rotor position signals output from the Hall ICs for each of the respective phases and rotor driving signals supplied to the stator coils for each of the respective phases. At the top, the inductance of each stator coil is shown in relation to the rotor position for each of the respective phases. In the second timing chart, the outputs of the Hall ICs (63u-63w) are shown for each of the respective phases according to the rotor position. If the rotor driving signals are supplied to the respective stator coils while the inductance of the respective stator coils is increasing, a torque (positive torque) is generated that causes the rotor to rotate in a first direction. On the other band, if the rotor driving signals are supplied to the respective stator coils while the inductance of the respective stator coils is decreasing, an opposite torque (negative torque) is generated that causes the rotor to rotate in a direction that is opposite to the direction that the rotor rotates when the positive torque is applied to the rotor.
In order to cause the rotor to rotate in the forward direction, the SR motor control circuit uses a forward rotation logic to control the timing of the rotor driving signals, which signals are supplied to the stator coils for each of the respective phases. The rotor driving signals are generated based upon the output signals of the Hall ICs 63u-63w for each of respective phases. For example, the rotor driving signals may be supplied to the U-phase coil, V-phase coil and W-phase coil in this order.
FIG. 6 also shows a timing chart for specific set of rotor driving signals to control the known SR motor. The rotor driving signal for the U-phase stator coil is initiated when Hall IC 63u detects the U-phase trailing edge signal. This U-phase rotor driving signal is terminated when Hall IC 63v detects the trailing edge signal of the V-phase. Similarly, the rotor driving signal for the V-phase stator coil is initiated when Hall IC 63v detects the V-phase trailing edge signal. This V-phase rotor driving signal is terminated when Hall IC 63w detects the trailing edge signal of the W-phase. Finally, the rotor driving signal for the W-phase stator coil is initiated when Hall IC 63w detects the W-phase trailing edge signal. This W-phase rotor driving signal is terminated when Hall IC 63u detects the trailing edge signal of the U-phase. In FIG. 6, when the rotor is rotating in the forward direction, the electrical angle is 0xc2x0 with respect to the forward rotating direction (clockwise direction in FIG. 5, right direction in FIG. 6).
In order to cause the rotor to rotate in the reverse direction, the SR motor control circuit uses a reverse rotation logic to control the timing of the rotor driving signals, which signals are supplied to the stator coils for each of the respective phases. The rotor driving signals are generated based upon the output signals of the Hall ICs 63u-63w for each of the respective phases. For example, the rotor driving signals may be supplied to the U-phase coil, W-phase coil and V-phase coil in this order.
The rotor driving signal for the U-phase stator coil is initiated when Hall IC 63u detects the U-phase leading edge signal. This U-phase rotor driving signal is terminated when Hall IC 63w detects the leading edge signal of the W-phase. Similarly, the rotor driving signal for the W-phase stator coil is initiated when Hall IC 63w detects the W-phase leading edge signal. This W-phase rotor driving signal is terminated when Hall IC 63v detects the leading edge signal of the V-phase. Finally, the rotor driving signal for the V-phase stator coil is initiated when Hall IC 63v detects the V-phase leading edge signal. This V-phase rotor driving signal is terminated when Hall IC 63u detects the leading edge signal of the U-phase. In FIG. 6, when the rotor is rotating in the reverse direction, the electrical angle is 0xc2x0 with respect to the reverse rotating direction (counterclockwise direction in FIG. 5, left direction in FIG. 6).
The start timing of the rotor driving signals supplied to the stator coils of respective phases (coil energizing start timing) may be advanced in order to improve motor operating efficiency. One method for advancing the start timing of the rotor driving signals includes providing the rotor position detectors in a position that is offset from the central position of a magnetic pole. Japanese Laid-Open Patent Publication No. 6-165464, for example, shows that this can be accomplished by advancing the position detectors by 30 electrical degrees. However, if only one offset rotor position detector is provided for each stator pole, the prior art has taught that the motor operating properties are different when the rotor is rotating in the forward direction as opposed to the reverse direction. Therefore, in these prior art systems it would be necessary to provide two rotor position detectors for each stator pole of a bi-directional motor, i.e., in both the forward rotating direction and reverse rotating direction of the rotor, each position detector being offset or shifted from the central position of the stator pole.
It is, accordingly, an object of the present invention to teach an improved synchronous motor and an improved control circuit for generating rotor driving signals that are supplied to the synchronous motor. By positioning the rotor position detectors appropriately, the number of rotor position detectors can be reduced as compared to the known reluctance motor described above. An advance angle can then be selected that will provide the same motor properties when the rotor is driven in the forward and reverse direction.
As a result of experiments that have been performed, it has been found that advancing a position detector a three-phase synchronous motor by an electrical angle of 30xc2x0 in one rotating direction from a central position of a stator pole and rotor driving signals can be advanced by the electrical angle of 30xc2x0 when the rotor rotates in both the forward direction and the reverse direction.
Consequently, the respective position detectors are preferably provided in positions that are advanced by an electrical angle of 30xc2x0 from central positions of stator poles of a stator core in one rotating direction. A driving circuit will then adjust the timing of the rotor driving signals that are supplied to each of the respective stator coils according to either a first logic or a second logic based on rotor position signals generated by the rotor position detectors. If only one rotor position detector is provided per stator coil, naturally the number of the position detectors can be reduced as compared to the known synchronous motor.
In another aspect of the present teachings, a delay circuit may be provided, which delay circuit delays the communication of the rotor position signals generated by the rotor position detectors to the control circuit. The control circuit will then adjust the timing of the rotor driving signals to be supplied to the respective stator coils for each of the respective phases based upon the rotor position signals that are delayed by the delay circuit.
Preferably, the delay time generated by the delay circuit varies in accordance with the rotating speed of the reluctance motor. In this case, the advance angle can always be controlled by the advance angle that maximizes motor efficiency. The delay time generated by the delay circuit also can be selected to compensate for a positional error caused by incorrectly mounting one or more of the rotor position detectors. If it is possible to compensate for mounting error, manufacturing tolerances can be relaxed and the rotor position detector mounting operation can be simplified.
In a further aspect of the present teachings, the control circuit may adjust the rotor driving signals according to a difference detected between a desired rotational speed reference signal and a detected rotational speed signal.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.